1. Field of the Invention
The invention relates to a no-go system for interfering with the downward movement of a tool, such as a safety valve, past a particular point in a landing nipple in a subterranean well, thereby accurately positioning the valve in the desired location.
2. Description of the Prior Art
No-go shoulders are used to positively position a device, such as a valve, within a landing nipple, for example. Known no-go systems comprise an integral, annular shoulder inwardly projecting from the inside cylindrical surface of a landing nipple. The inside diameter of the no-go shoulder is large enough to permit passage of necessary wire line tools, but small enough to interfere with an outwardly projecting no-go shoulder formed on a safety valve, or other tool to be positioned by the no-go system.
Such conventional systems accurately position a tool in a landing nipple, and also provide contact surfaces for transmission of jarring forces. However, in the prior art, design compromises have been necessary. On one hand, the no-go shoulder on the nipple must be small enough to permit tools to bypass it, and to present minimum restrictions to production flow. On the other hand, the shoulder must be large enough to effectively interfere with the downward movement of the valve or other tools to be positioned, and to sustain large jarring forces. Inwardly projecting no-go shoulders as described are subject to wear caused by wire line tools passing across the shoulder when the valve is out of position, as during operations for running and retrieving other valves or plugs. In some instances, the inwardly projecting shoulders have been worn to the extent that they have failed to resist downward movement of the valve during downward jarring, thereby permitting the valve to become jammed in the no-go shoulder.